The present invention relates to ground surveillance Doppler radar making it possible to detect or locate moving targets travelling on the surface of the ground between natural obstacles, which cause fixed echoes.
In known manner, such a Doppler radar transmits recurrent pulses and receives these pulses after reflection on a large number of obstacles located in the scanning field of the transmitting-receiving antenna.
A double processing of these signals is performed in order to locate interesting moving targets. Firstly, a system of gates is used, which subdivides the signal received in time, so as to discriminate a series of areas distributed in a regular manner in the field under surveillance. In certain very simplified cases, a single gate is used, which defines a range of given depth, which can be displaced at random by the operator in the field of range of the radar.
This is followed by a frequency analysis on the signals from a group of successive pulses in order to obtain a spectrum corresponding to a moving object having a given radial speed and located in the sector corresponding to the selected gate.
The signal from the spectrum analyzer is processed in a threshold circuit in order to discriminate this signal from the noise. The output signal from the discriminator is a binary signal which, for each successive distance gate, gives an information bit, whose value indicates a detection or a nondetection. These signals are processed and applied to a display means making it possible to locate the thus detected moving targets. However, among the detected targets, certain of them have a relative danger as a function of the distance at which they are located and as a function of the radial speed at which they travel, whereby said two criteria can be combined. The display means used for this type of radar do not reveal this danger.